The present invention relates to wireless communication devices capable of communicating through a plurality of wireless communication networks which operate under different communication protocols, and operating with different battery power consumption rates.
Various kinds of wireless communication devices are used for mobile communications. The devices include, for instance, personal digital cellular (PDC) type phones such as a cellular phone and a car phone, and personal handy phone (PHS) type devices developed as the second generation cordless phone.
The PDC phone is capable of providing communication services over a wide area because the service area of its base station (BS) is from 1.5 kilometers to several kilometers (macro cell) in radius, and is capable of providing communication services even when phone users are moving at high speeds. However, the cellular phones and the car phones consume more electric power, because a comparatively high transmission output power is required.
On the contrary, the PHS phone provides communication services over a limited area because the service area of its cell station (CS) is from 100 meters to several hundred meters (micro cell). The PHS phones consume less electric power, because a comparatively low transmission output power is required. However, the PHS phone is not capable of providing its services when phone users are moving at high speeds.
New type of cellular phones which are compatible with both the PDC phones and the PHS phones are proposed so that such phones are operable under different communication modes, that is, under the PDC communication protocol and the PHS communication protocol.
If such a cellular phone operable under both PDC protocol (PDC mode) and PHS protocol (PHS mode) is connected to the PDC communication network and operates under the PDC communication protocol, it consumes more electric power because of its high transmission output power. The electric energy of a built-in battery is consumed rapidly when a phone talk or a transmission of a large amount of data continues for a long period of time. The remaining capacity of the battery decreases quickly, occasionally resulting in that the talk or data transmission is disabled unexpectedly.
It is therefore an object of the present invention to provide a wireless communication device which is capable of avoiding unexpected disablement of communication even when a remaining power of a battery decreases rapidly in the course of communication.
According to the present invention, a wireless communication device is operable with a built-in battery and in different communication modes. The wireless communication device includes a first communication part capable of communication through a first external communication network under a first communication mode, and a second communication part capable of communication through a second external communication network under a second communication mode which is less power-consuming than the first communication part. When a battery power decreases too much, an operable communication part of the wireless communication device is switched from the first communication part to the second communication part thereby to connect the second communication part to the second external communication network and disconnect the first communication part from the first external communication network, thereby reducing the power consumption of the battery.